[bug report] iommu_dma_unmap_sg() is very slow then running IO from remote numa node

[Ming Lei]

On Wed, Jul 21, 2021 at 10:23:38AM +0100, John Garry wrote:
> On 21/07/2021 02:40, Ming Lei wrote:
> > > I think that you should see a significant performance boost.
> > There is build issue, please check your tree:
> > 
> >    MODPOST vmlinux.symvers
> >    MODINFO modules.builtin.modinfo
> >    GEN     modules.builtin
> >    LD      .tmp_vmlinux.btf
> > ld: Unexpected GOT/PLT entries detected!
> > ld: Unexpected run-time procedure linkages detected!
> > ld: drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.o: in function `smmu_test_store':
> > /root/git/linux/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c:3892: undefined reference to `smmu_test_core'
> >    BTF     .btf.vmlinux.bin.o
> > pahole: .tmp_vmlinux.btf: No such file or directory
> >    LD      .tmp_vmlinux.kallsyms1
> > .btf.vmlinux.bin.o: file not recognized: file format not recognized
> > make: *** [Makefile:1177: vmlinux] Error 1
> 
> Ah, sorry. I had some test code which was not properly guarded with
> necessary build switches.
> 
> I have now removed that from the tree, so please re-pull.

Now the kernel can be built successfully, but not see obvious improvement
on the reported issue:

[root at ampere-mtjade-04 ~]# uname -a
Linux ampere-mtjade-04.khw4.lab.eng.bos.redhat.com 5.14.0-rc2_smmu_fix+ #2 SMP Wed Jul 21 05:49:03 EDT 2021 aarch64 aarch64 aarch64 GNU/Linux

[root at ampere-mtjade-04 ~]# taskset -c 0 ~/git/tools/test/nvme/io_uring 10 1 /dev/nvme1n1 4k
+ fio --bs=4k --ioengine=io_uring --fixedbufs --registerfiles --hipri --iodepth=64 --iodepth_batch_submit=16 --iodepth_batch_complete_min=16 --filename=/dev/nvme1n1 --direct=1 --runtime=10 --numjobs=1 --rw=randread --name=test --group_reporting
test: (g=0): rw=randread, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) 4096B-4096B, ioengine=io_uring, iodepth=64
fio-3.27
Starting 1 process
Jobs: 1 (f=1): [r(1)][100.0%][r=1503MiB/s][r=385k IOPS][eta 00m:00s]
test: (groupid=0, jobs=1): err= 0: pid=3143: Wed Jul 21 05:58:14 2021
  read: IOPS=384k, BW=1501MiB/s (1573MB/s)(14.7GiB/10001msec)

[root at ampere-mtjade-04 ~]# taskset -c 80 ~/git/tools/test/nvme/io_uring 10 1 /dev/nvme1n1 4k
+ fio --bs=4k --ioengine=io_uring --fixedbufs --registerfiles --hipri --iodepth=64 --iodepth_batch_submit=16 --iodepth_batch_complete_min=16 --filename=/dev/nvme1n1 --direct=1 --runtime=10 --numjobs=1 --rw=randread --name=test --group_reporting
test: (g=0): rw=randread, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) 4096B-4096B, ioengine=io_uring, iodepth=64
fio-3.27
Starting 1 process
Jobs: 1 (f=1): [r(1)][100.0%][r=138MiB/s][r=35.4k IOPS][eta 00m:00s]
test: (groupid=0, jobs=1): err= 0: pid=3063: Wed Jul 21 05:55:31 2021
  read: IOPS=35.4k, BW=138MiB/s (145MB/s)(1383MiB/10001msec)


Thanks, 
Ming